1. Field of the Invention
The present invention relates to laser gyroscopes and more particularly to the geometric improvements therein.
2. Description of the Prior Art
In accordance with the present state of the art a laser gyroscope combines the operative characteristics of an optical resonator (laser) with relativistic effects to provide an instrument sensitive to angular rotation. The optical resonator is typically formed by a combination of a gain medium with reflective surfaces which, in the case of a laser gyroscope form a ring comprising three or more mirrors. These mirrors then set an optical path length which sets the frequency at which the resonator operates. The resonant wavelength, and thus frequency, for each beam is determined by the condition that an integral number of wavelengths fit exactly along the cavity perimeter. Rotation in inertial space about a line perpendicular to the plane of the cavity causes the cavity perimeter to exhibit differing lengths for the two opposite directions of optical beam propagation. Thus, the two beams have different frequencies which when superposed forms a beat frequency. This beat frequency or difference between frequencies is in proportion to the rate of rotation providing a measurement of the angular rate in inertial space.
In this form the beat frequency .DELTA.f has a relationship to the angular rate w as follows: EQU .DELTA.f.congruent.4Aw/lL
where A is the area enclosed by the optical ring, l is the resonating wave length and L is the perimeter length of the oscillating cavity. Since the wave length l is essentially a function of harmonics within the cavity length L the gain or sensitivity resolves as follows: EQU .DELTA.(f/w);=k(A/L)
Thus the maximum geometric gain effect is that of a circle.
In this form the ring laser gyroscope comprises two oscillators in a single cavity where the cavity length provides a direct effect on the gyro sensitivity or the net frequency differential (beat frequency) in response to angular rate. Like all oscillators operating in a single enclosure, ring lasers exhibit the characteristics of "mode pulling" and "lock in" where a certain dead band is inherent, i.e., a minimal frequency difference, which, once again, falls off with the area enclosed by the beam path. Accordingly, both the gain and dead band relate directly to the area enclosed and optimization of the area thus optimizes the gyroscope.
One aspect of lock-in is associated with the two linear polarization components, referred to as the S & P components, of the electromagnetic wave, respectively perpendicular and parallel to the ring laser plane. This polarization is such as to result in 0 degree phase shift at a mirror for the S component and 180 degree phase shift for the P component. There is therefore a 180 degree phase shift decoupling associated with all odd number mirror configurations.
Since the lasing or gain medium typically entails a plasma discharge one further phenomenon of lasers is magnetic sensitivity, expressed by the Zeeman effect wherein the magnetic field causes the excited electrons to split into two energy levels. This Zeeman splitting then causes a phase shift which is indistinguishable from frequency change with rotation.
Accordingly, a variety of phenomena encumber the operation of a ring laser, phenomena addressed in the past with singular solutions which often have not achieved complementary accommodation. A singular approach resolving all the foregoing phenomena has been sought in the past and it is one such approach that is disclosed herein.